Molybdenum nitriding steels and process of nitriding same



latented Aug. 6, 19 29.

n'irsn STATES TENT OFFICE.

HENRY A. DE FRIES, 0F ALBANY, NEW YORK, ASSIGNOR TO LUDLUM STEEL COMPANY, OF WATEBVLIET, NEW YORK, A CORPORATION OF NEW JERSEY.

IVIOLYBDENUM NITRIDING STEELS AND PROCESS OF NITRIDING SAME.-

No Drawing.

My present invention relates to molybdenum steels for purposes of nitriding and the process of nitriding such steels.

The nitriding of steels containing aluminum together with other alloying constituents, usually chromium and also containing carbon in relatively small percentages presents, as has been heretofore practiced, a considerable diliiculty, especially in the production of such aluminum bearing steels.

In the production of such aluminum hearing steels special methods have tobe followed which occasion difiiculties in manufacture and the so-called alligator skin phenomenon characteristic of aluminum bearing steels has to be contended'With. These alligator skins form on the outside of the ingots, necessitating an extra rough turning of the ingots of aluminum bearing steel and for these and other reasons it is desirable, so far as possible, to avoid the inclusion of aluminum in any considerable percentage in steels that are intended for later being subjeetedto a nitriding treatment. e,

According to the present invention, alumimum is practically entirely or completely dispensed with as an alloying material in steel and, if present at all, is only in minute quantities.

Steels containing no, or practically no aluminum, and containing fairly considerable proportions of molybdenum, say of the order of 15% up to around 2%, can be readily manufactured by ordinary electrical and open hearth manufacturing processes and none of the difficulties such as alligator skin troubles, characteristic of aluminum bearing steels, are encountered in the manufacture.

The nitriding steel of the present invention, in addition to containing molybdenum, may contain various other alloying elements as manganese, nickel, vanadium, chromium, tungsten, silicon, etc.

()ne molybdenum bearing steel Which can be nitrided to good advantage by subjection to a nitrogen atmosphere at a temperature around 900 F., and preferably between 875 Application 'filed March 2,

Remainder iron.

This steel was nitrided at 930 F. for a period of ninety hours and showed a deep file hard case; the core of this steel was tough. Upon attempting to produce a nitrided case on similar steel containing no molybdenum and which was of the following analysis:

Per cent. Carbon 0.45 Manganese .30 Chromium 8.50 Silicon 3.50

Remainder iron,

which is commercially known as Silcrome No. 1, the steel, after a treatment identical to that to which the foregoing molybdenum containing steel was subjected, was soft and ductile and no surface hardening effect could be discerned.

The molybdenum bearing steels for nitriding, according to my invention, can contain varying quantities of carbon according to the desired core hardness required, and the carbon content may range from about 10% up to about 2%, preferably under 1%. I have found that the molybdenum steels for nitriding, in accordance with my invention and as above described, produce a fairly ductile and hard nitrided case as long as thenitriding temperature is kept below the formation point of any carbo-nitrides. lVhen the source of nitrogen for nitriding is from disassociation of ammonia, the temperature for nitriding is, of course, kept sufficiently above the disasseciation temperature of the ammonia to furnish the requisite supply of nitrogen.

When chromium is used in nitriding steel,

a desirable range is about 1% to 9%, and for.

silicon when used, from about .5 to about 2. As a new article of manufacture, a steel 3.50%. article'composed of steel containing about I claim: 8% of chromium, about 1.5% of silicon, about 1. As a new article of manufacture, a steel .7 0% of molbdenum, about .1 to 1% of car- 5 article composed of steel containing about bon, and substantially free from aluminum 15 1 to 9% chromium, about .50 to 3.50% of and having anitride hardened surface. silicon about .15 to 2% of molybdenum, about In testimony whereof, I have signed my .1 to 1% of carbon, and substantially free name hereto.

from aluminum and having a nitridehard- 10 ened surface. 7 HENRY A. DE FRIES. 

